The Ghosts of Berkeley Square (1947)

Classic British supernatural-comedy film, starring Robert Morley and Felix Aylmer. Two 18th century officers desperate to prevent war, hatch a plan to capture the Duke of Marlborough and hold him prisoner until the threat of hostilities passes. But whilst testing the contraption they've designed to trap him - they manage to kill themselves!! Their stupidity incurs the wrath of Queen Anne in the afterlife, so as a punishment they're condemned to haunt the Berkeley Square house until a British monarch enters it..! NOTE - I believe this film to be in the public domain.